Fragrances are of great interest especially in the field of cosmetics and also laundry and cleaning detergents. Fragrances of natural origin are mostly expensive, often limited in their available amount and, on account of fluctuations in environmental conditions, are also subject to variations in their content, purity etc. It is therefore of great interest to be able to replace, at least partially, fragrances of natural origin with synthetically obtainable substances. Often, in this connection, the natural substance is not replicated chemically, but chemically synthesized compounds are selected as substitutes for natural substances on account of their odor, where substitute and natural substance do not necessarily have to have a chemical- structural similarity.
However, since even small changes in chemical structure may bring about massive changes in the sensory properties such as odor and also taste, the targeted search for substances with certain sensory properties, such as a certain odor, is extremely difficult. The search for new fragrances and flavorings is therefore in most cases difficult and laborious without knowing whether a substance with the desired odor and/or taste will even actually be found.
Diesters of unsaturated and saturated 2,5-dimethyladipic acids and their preparation are generally known in the state of the art.
U.S. Pat. No. 2,244,487 discloses dimethyl (E)-2,5-dimethyl-2-hexenedioate, isolated from high-boiling residues obtained in the manufacturing process of methyl methacrylate using acetone and hydrogen cyanide as raw materials. It is suggested that (E)-2,5-dimethyl-2-hexenedioate can be used for the preparation of resins, plasticizers and as starting material for the preparation of other esters of (E)-2,5-dimethylhex-2-enedioic acid, which in turn are of interest as plasticizers, modifiers or blending agents for synthetic or natural resins.
FR 2 524 341 discloses a palladium catalyst, in form of a allylic cationic complex, for the use in the dimerization or co-dimerization reactions of acrylic acid derivatives with themselves or with mixtures of other di-functional components, such as 1,3-dienes. Besides other dimerization products, the preparation of dimethyl 2-hexendioate from methyl acrylate as well as the preparation of dimethyl 2-methyl-5-methylene-hexanedioate from methyl methacrylate, where dimethyl (E)-2,5-dimethyl-3-hexenedioate was formed as a side product, using the claimed palladium catalyst are exemplified.
DE 3336691 discloses a process for the nickel catalyzed dimerization of acrylic acid derivatives to yield linear unsaturated dicarboxylic acids derivatives and the use of these dicarboxylic acid derivatives as monomers and/or co-monomers in polymer, polycondensation and hydration reactions.
U.S. Pat. No. 4,451,665 discloses a process for dimerizing a lower alkylacrylate or a lower alkyl-methacrylate in the presence of a palladium (II) catalyst to yield mixtures of isomeric linear dimers. In particular, this reaction was used for the preparation of mixtures of linear isomeric dimethyl hexenedioates and dimethyl 2,5-dimethylhexenedioates.
EP 0 632 010 discloses a process for the preparation of dimethyl esters of alpha,omega-dicarboxylic acids from cycloalkanones with dimethylcarbonate in the presence of a nitrogen containing base. Besides the preparation of other dimethyl esters of alpha,omega-dicarboxylic acids, the preparation of the dimethyl ester of 2,5-dimethyladipic acid from 2,5-dimethylcyclopentanone and dimethylcarbonate is exemplified.
Narushi et al., Nippon Kagaku Kaishi 1976, Vol. 11, pp.1794-6, relates to the identification of α-methylene-δ-methyladipic acid (2-methyl-5-methylene-hexanedioic acid) as the main product of a dimerization process comprising the thermal dimerization of calcium methacrylate (monomer salt) followed by treatment of the obtained acidic dimerization products with diazomethane.
Matsuoka et al., Org. Lett. 2011, Vol. 13(14), pp. 3722-5, disclose a process for the selective tail-to-tail dimerization of methyl methacrylate in the presence of an N-heterocyclic carbene catalyst, yielding dimethyl 2,5-dimethyl-2-hexenedioate with an E/Z ratio of 95:5.
Biju et al., Angew. Chem. Int. Ed. Engl. 2011, Vol. 50(36), pp. 8412-5, disclose a process for the coupling of two activated olefins in the presence of an N-heterocyclic carbene catalyst. Their optimized process allows the production of dibutyl 2,5-dimethyl-2-hexenedioate from dibutyl methacrylate with an E/Z ratio of 97:3.
JP 54092636 discloses fragrant compositions containing di-(C1-C10)-esters of α-methylene-δ-methyladipic acid (2-methyl-5-methylene-hexanedioic acid) as an effective component. Esters of 2,5-dimethylhexenedioic acids or 2,5-dimethyladipic acid are not mentioned.